Manipulating Phase

Last month, we learned about the waveform displays in editors and oscilloscopes. This time, we’ll explore practical applications for one of the most misunderstood elements of audio—phase.

Fig. 1

Simply put, the phase of a waveform determines the point where its cycle begins, whether it is a sample or a single-cycle wave. Figure 1 shows how phase is measured in degrees, with the four most common angles of phase—0º, 90º, 180º, 270º, and back to 0º (or 360º)—highlighted. Of course, summing two identical waveforms that are 180º out of phase will cancel the audio completely, if their levels are identical. However, phase can be used creatively when it is altered less drastically. Here are four examples.

TIMBRE SHIFTS

Fig. 2

Many soft synths, such as Sylenth1, Operator, and Serum (Figure 2) include adjustable phase for their waveforms. As described above, adjusting the phase of a waveform simply changes the point where its cycle begins. On its own, with no other oscillators, this will have no audible effect on the sound of a waveform. The trick is to adjust the phase in relationship to a second oscillator or audio source. A cool experiment that yields immediate results is to put a saw-tooth (all integer harmonics) on oscillator 1 and a square (only odd-numbered harmonics) on oscillator 2, then put oscillator 2 180º out of phase. The result? Only even-numbered harmonics, as the odd harmonics cancel.

ATTACK TRANSIENTS

Fig. 3

Generally speaking, when editing sample data, it’s important to look for zero-crossing points to avoid clicks or pops. And therein lies another phase-related technique: You can add transients to a sound by moving its start point off of the zero-crossing. This is one of the secret tricks of IDM and experimental tracks. To get a feel for this approach, take an 808 kick, which has a lot in common with a sine wave, and move its start point to the peak of the first cycle (Figure 3). You’ll hear a click at the beginning of the sound, which can then be adjusted to taste. This technique works great with bass sounds, too.

CENTER-CHANNEL KILL SWITCH

Fig. 4

The classic karaoke technique of removing vocals from an existing track is based on a very simple phase trick of putting one channel 180 degrees out of phase with the other. This works because vocals are often in the exact center of their mix, which means they are present in both the left and right channels. To hear this in action, begin with a stereo track (older music works best because panning techniques were more extreme in the golden age of radio). Flip the phase of one of the channels, and then sum it to mono. Figure 4 shows this process using two Ableton Live Utility devices.

BLENDING BASS AND KICK

Getting the bass and kick to sit properly in a mix is often accomplished using sidechain compression, but here’s an additional trick I learned from techno producer Matt Lange. Once you have your bass and kick sitting nicely in your mix, flip the phase of either the bass or the kick. Sometimes, it will instantly clean up the low-end. (Other times, it will actually make things worse.) But when you test this on the low-end of your mix, you’ll instantly know which is the better option—and it can work wonders.